1. HILL RESEARCH LAB Isoprene Analysis by Ion Mobility Spectrometry-Mass Spectrometry INTRODUCTION RESULTS Isoprene is one of the most important naturally emitted volatile organic compounds (VOC) in the atmosphere. It accounts for more than a third of globally annual VOC emissions. It plays a significant role in atmospheric photochemistry through facilitating the production of pollutants such as ground level ozone and secondary organic aerosols. Detecting isoprene in ambient air requires continuous measurement with sub ppbv detection limit, a large linear dynamic range, and a high selectivity. For micrometeorlogical flux measurements atop forest canopies, fast instrument response of 10 analysis per second is necessary. This study aims to demonstrate that IMS alone can be used for field flux measurements to rapidly detect and separate isoprene from monoterpenes. METHODS Figure 6. Mass-selected ion mobility spectra of isobaric isoprene dimer,  -pinene and myrcene at 200ºC (R p 75) and 150 ºC (R p 85) Head space sample vapor was directed into the ion mobility spectrometer (IMS) by a flow of nitrogen gas and ionized by secondary electrospray ionization (SESI). The samples analyzed were isoprene, myrcene,  -pinene, R-(+)-limonene, and 3-carene. The structures of these compounds are shown on the right. The ion mobility spectrometry-mass spectrometry (IMS- MS) system consisted of an electrospray ionization (ESI) source, an IMS coupled to a 150 QC ABB Extrel quadrupole mass spectrometer (QMS), or an Ionwerks orthogonal time-of-flight mass spectrometer (TOF-MS). Experimental data demonstrated the ability of IMS to separate isoprene and monoterpenes. The monomeric isoprene (K 0 = 2.35 cm 2 V -1 s -1 ) was observed for the first time by IMS (Figure 2). Dimer, trimer, and tetramer ions of isoprene were also detected. Pentamer ions were observed at higher sample concentrations (Figure 3). The mass-mobility trend line of isoprene ions is shown in Figure 4. The mobility time of the four monoterpenes analyzed were very similar (Figure 5). Separation between monoterpenes would require ultra-high resolution-IMS. As the IMS temperature decreased, the resolving power (Rp) of IMS increased, allowing for the separation of the isobaric isoprene dimer and monoterpenes (Figure 6). Figure 4. 2D-IM-MS plot of isoprene ions, shown with mobility drift times and mass-to- charge ratios Figure 2. Mass-selected ion mobility spectra of isoprene at low concentration Figure 3. Mass-selected ion mobility spectra of isoprene at high concentration Isoprene 68Da Myrcene 136 Da  -Pinene 136 Da R-Limonene 136 Da Figure 5. Ion mobility spectra of isobaric monoterpenes at 200 º C 3-Carene 136 Da CONCLUSION Department of Chemistry Hill Research Group Ion Mobility Spectrometry Monomer Dimer Trimer Figure 1. Ion mobility spectrometer coupled to a time-of-flight mass spectrometer ABOUT THE PROJECT A stand-alone IMS has the capability of separating isoprene from monoterpenes, with fast signal response that is suitable for micro-meteorlogical flux measurements. This is a multidisciplinary project in collaboration with Dr. Hal Westberg and Jack Chen, from the Department of Civil and Environmental Engineering. The project involves measuring and modeling biogenic Volatile Organic Compounds (BVOC) emissions from vegetation. The goal is to understand the role of BVOC in regional atmospheric chemistry and terrestrial carbon exchange related to the global carbon cycle and climate change. Camping trip with collaborators